1. Field of the Invention
The present invention relates to an ink cartridge used in an ink jet printing device, and more particularly, to an ink cartridge with an ability to adjust internal fluid pressure automatically.
2. Description of the Prior Art
As personal computers become more popular, ink jet printing devices are becoming a most common computer output/printing device used by people, families, and companies, because a price and a quality of the ink jet printers attract customers to buy.
A typical ink jet printing device has a printing head that moves along a track, back and forth, to print on a document. The printing head usually has at least an ink cartridge, and the ink cartridge comprises a housing with an ink reservoir for storing ink, and a print head connected to the ink reservoir to control the ink jetting. In a typical ink jet printing device, flow control is usually employed to control the ink jetting out to the document from the ink reservoir. Typical print head flow control mechanisms are divided into two types: thermal-bubbles and pressure-waves.
The thermal-bubbles print head comprises a thin-film resister. When the resistor is heated, a trace of ink vaporizes immediately, quickly expanding to make ink pass through the print head, and print on the document. Although the print head using the flow control can get ink from the ink reservoir and jet ink effectively, the flow control needs a controlling mechanism, so that the print head does not seep ink when not in use. The controlling mechanism usually provides a light negative pressure to prevent ink from seeping onto the print head. The negative pressure is partial vacuum in the ink cartridge, so that the external atmospheric pressure is slightly higher than the fluid pressure us in the ink cartridge. The negative pressure is indicated by a positive value, so an increase in the negative pressure means an increased vacuum of the ink cartridge, and a greater difference between the external atmospheric pressure and the fluid pressure in the cartridge. By increasing the negative pressure, ink is prevented from seeping from the print head.
Although increasing the negative pressure prevents ink from seeping out of the print head, the negative pressure has an upper limit. If the negative pressure is too high, ink cannot overcome the negative pressure and jet from the print head. On the other hand, the ink cartridge must be able to adjust the negative pressure in the ink reservoir automatically by changing the pressure of the surrounding environment to maintain a suitable range. For example, when the pressure of the surrounding environment decreases, the negative pressure causing ink not to seep through the print head is higher. Furthermore, the xe2x80x9coperating-effectxe2x80x9d of the ink reservoir also affects the negative pressure of the ink reservoir. For example, when the ink in the ink reservoir is continually consumed, the negative pressure of the ink reservoir increases. At this time, unless the negative pressure is adjusted appropriately, the print head ejects less ink, which affects the printing quality, such that the print head may not even jet ink any more.
In the prior art, the negative pressure of the ink reservoir is controlled by a xe2x80x9cregulatorxe2x80x9d in the ink reservoir. The regulator is usually an elastic air bag. By stretching the elastic air bag between a maximum volume and a minimum volume, the volume of stored ink in the ink reservoir also changes to adjust to changes of the negative pressure. For example, when the pressure of the surrounding environment decreases, the negative pressure of the ink reservoir also decreases. At this time, the regulator starts to increase the volume used for storing ink in the ink reservoir. Therefore, the negative pressure is increased, and the ink does not seep.
A major shortcoming of the prior art elastic air bag regulator is that the maximum volume of the elastic air bag has limits. When ink is consumed to a predetermined degree, and the elastic air bag expands to the maximum volume, the volume of stored ink in the ink reservoir does not change any more. Continued reduction of ink volume causes the negative pressure to exceed the range, and the ink does not overcome the negative pressure to jet from the print head, such that the ink in the ink trough is not used completely and is wasted.
Another kind of prior art used to control the negative pressure in the ink trough is a bubble generator. As disclosed in U.S. Pat. No. 5,526,030, the bubble generator is set in the ink reservoir and has a jet hole through the housing of the ink cartridge. With the jet hole, external air can enter into the ink reservoir. The controlling mechanism in the bubble generator designed appropriately makes ink gather in the jet hole and utilizes the capillarity of ink to form a liquid seal. When the negative pressure of the ink reservoir rises to a predetermined degree, external air overcomes the liquid seal and enters into the ink reservoir as a bubble. Thus, the negative pressure of the ink reservoir decreases. Furthermore, as a result of the bubble entering into the ink reservoir and negative pressure reducing, the liquid seal of the jet hole rebuilds to prevent bubbles from continuing entering.
However, the bubble generator above uses surface tension of ink and static water pressure of ink to control bubbles entering into the ink reservoir. Therefore, the primary shortcomings of the prior art above are: 1.) When using different ink, the surface tension of ink is different, and the bubble generator needs to be redesigned; 2.) When remaining ink is reduced, static water pressure of the ink changes, and an pressure adjusting capability of the bubble generator is limited. 3.) For a negative pressure of the ink reservoir as bubbles enter being the designed value, the bubble generator must be designed precisely, increasing the difficulties of manufacturing and assembling.
It is therefore a primary objective of the present invention to provide an ink cartridge with an ability to adjust pressure automatically, regardless of atmospheric pressure effects.
According to the claimed invention, the ink cartridge comprises a housing with an ink reservoir for storing ink. The housing has a first vent, a second vent and an opening. The opening is installed at a bottom end of the housing and is connected to the ink reservoir. The ink cartridge further comprises an air bag installed in the ink reservoir and connected to the first vent. The first vent enables external air to enter the air bag, and the air bag adjusts pressure within the ink reservoir. An elastic restricting device is installed in the ink reservoir for restricting air in the air bag, to prevent the ink in the ink reservoir from seeping through the opening. An elastic plugging device elastically plugs the second vent of the housing. And, an active shaft is movably installed in the ink reservoir for pushing the elastic plugging device. Consumption of the ink in the ink reservoir causes the air bag to expand. When the air bag expands to a predetermined degree, the air bag moves the active shaft, the active shaft pushes the elastic plugging device, and air enters into the ink reservoir through the second vent to reduce the volume of the air bag. When the air bag stops moving the active shaft, the elastic plugging device elastically plugs the second vent.
It is an advantage of the claimed invention that the ink cartridge can adjust internal pressure within the ink reservoir.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.